The Niagara River, which feeds the falls, drains four of the five Great Lakes and sends an average of 6 million cubic feet of water over the cataract every minute. This natural spectacle is shared between the United States and Canada, making its management a matter of international agreement. While the falls appear to be an unstoppable force of nature, human engineering has demonstrated the ability to temporarily manipulate this powerful flow.
The Historical Fact: Stopping the American Falls
In 1969, the U.S. Army Corps of Engineers successfully dewatered the American Falls. This project was undertaken to allow a geological survey of the rock face and riverbed, which had become threatened by accumulated rockfall. Concerns had grown following significant rockslides in the preceding decades, which left a pile of debris, known as talus, at the base of the falls.
To divert the water, engineers constructed a temporary barrier called a coffer dam. The dam stretched 600 feet from the American mainland to the upstream end of Goat Island. This involved dumping approximately 28,000 tons of rock and earth into the Niagara River over three days in June 1969. The coffer dam redirected the entire flow toward the larger Horseshoe Falls, leaving the American Falls completely dry for the first time in an estimated 12,000 years.
With the falls silenced, geologists walked on the exposed riverbed to conduct a detailed study of the underlying rock structure. They drilled deep into the bedrock to extract core samples and installed instruments to measure rock stress and movement. The investigation revealed that the talus pile at the base, which had been considered unsightly, was actually providing structural support to the cliff face.
Based on these findings, the International Joint Commission decided against removing the majority of the talus, determining that its removal could destabilize the upper layer of the falls. Engineers used the opportunity to stabilize the exposed rock face with steel bolts, cables, and anchors inserted into the cliff. After nearly six months of study and stabilization work, the coffer dam was dismantled in November 1969, allowing the water to rush back over the American Falls.
Modern Water Control and Diversion for Power
Today, the entire Niagara River is continually managed by a permanent system of control structures and international agreements. This control is governed by the 1950 Niagara River Water Diversion Treaty between the United States and Canada. The treaty balances the preservation of the scenic spectacle with the potential for hydroelectric power generation. It stipulates specific minimum flow requirements to ensure the falls retain their visual splendor, particularly during peak tourist hours.
During the tourist season (April 1st to October 31st), the treaty mandates that a minimum of 100,000 cubic feet of water per second must flow over the falls during daylight hours. This flow is reduced by half to 50,000 cubic feet per second at night and during the winter months. Any water volume exceeding these minimum scenic flow requirements is diverted upstream of the falls and channeled for generating electricity.
The primary mechanism for this daily water management is the International Niagara Control Works. This structure, located about a half-mile upstream of the Horseshoe Falls, uses movable gates. The control dam is jointly operated by the New York Power Authority and Ontario Power Generation to ensure treaty-mandated flow requirements are met. The system of intakes and underground tunnels then diverts the excess water to power stations on both the American and Canadian sides of the river.
This engineering allows the two nations to utilize a significant portion of the river’s volume for power generation, with the excess water equally divided between them. The permanent diversion of water for hydroelectricity is so effective that only a fraction of the river’s natural volume passes over the falls, even during peak flow periods. This continuous, managed diversion ensures that while the falls are never fully “turned off,” their flow is constantly regulated to meet both economic and aesthetic demands.